1. Field of the Invention
This invention relates to an apparatus for digitally measuring the configuration of a lens frame of an eyeglass frame or the configuration of a template obtained by copying the lens frame, and more particularly to a lens frame configuration measuring apparatus suitable for use in combination with a lens grinding machine for grinding an optical lens blank in accordance with data concerning the configuration of the lens frame or template.
2. Description of the Prior Art
As shown in FIG. 37(a), in a typical conventional apparatus for measuring the configuration of a lens frame, right and left lens frames (frame rims) 3, 3 of an eyeglass frame 2 are first brought into contact with a holding surface 1 (measuring surface) of a frame holding device, not shown, and are maintained thereon by a maintaining rod, not shown, biased by a spring. Thereafter, a beveled feeler 5 is brought into contact with a V-shaped groove 4 of the lens frame 3 and moved along the groove 4, so that the track of the feeler is three-dimensionally detected to measure the configuration of the lens frame 3 of the eyeglass frame 2.
Generally, the front of the eyeglass frame 2 is curved as shown in FIG. 37(a). For this reason, part 7 of the lens frame 3 close to a temple (sidepiece) of the eyeglass frame 2 is spaced from the holding surface 1 (measuring reference surface) when part of the lens frame 3 close to a bridge 6 of the lens frames 3, 3 maintains contact with the surface 1 by means of the maintaining rod, not shown. As a result, the lens frame 3 and the holding surface 1 are inclined relative to each other.
In order to measure the accurate size and shape (true size) of the lens frames 3, 3, a coincidence is required between angle .gamma. and angle .delta.. As shown in FIG. 38(b), .gamma. is an angle formed by a plane including the apex of the edge of a lens L and a center line passing through the V-shaped groove of the lens frame, whereas .delta. is an angle formed by a plane including the apex of the feeler and the center line passing through the V-shaped groove of the lens frame.
However, in the conventional apparatus for measuring a lens frame configuration, the V-shaped feeler 5 is rotatably held by a measuring shaft (not shown) of a measuring head section for rotation about an axis 0 perpendicular to the holding surface 1 as shown in FIG. 37(b). For this reason, the V-shaped feeler 5 is in contact with the V-shaped groove 4 at an angle of inclination .gamma. with respect to an extending direction of the V-shaped groove 4 as shown in FIG. 37(b) and therefore, it has parts which are in contact with intermediate parts of slanted surfaces 4a, 4a of the V-shaped groove 4 as shown in FIG. 37(c).
As a consequence, for measurement, the apex 5a of the feeler 5 becomes impossible to be in contact with the root of the V-shaped groove and is, therefore, obliged to be moved along the V-shaped groove copying the contour thereof with the apex 5a apart from the root. Sometimes, it happens that the feeler 5 is completely disengaged from the V-shaped groove 4. As a result, an accurate measurement of the lens frame 3 cannot be obtained.
This inconvenience is attributable to the fact that the feeler 5 is incapable of rotating in a direction perpendicular to the axis 0 (rotational axis) and incapable of copying the contour of the curved lens frame 3.
In case a lens L is ground based on measurement data thus obtained, a finished size of the ground lens L unfavorably becomes smaller than the true size as shown in FIG. 38(c).
That is, the angles .gamma. and .delta. are not in agreement with each other due to inclination of the curved lens frame. If the lens L is ground based on incorrect data obtained at the area of the apex of the feeler, the lens L is ground to have, as an outer diameter, a size c different from a true size d thereof, as shown in FIG. 38(a). As a result, the finished lens L of the size c does not fit the lens frames 3, 3 of the size d, as shown in FIG. 38(c).
Also, as shown in FIG. 37(a), part 7 (part where the temple is attached as an ear hanger) of the lens frame 3 opposite to the bridge 6 is held in a state apart from the holding surface 1. If this spaced-apart amount is large, there is a possibility that the feeler 5 is disengaged from the V-shaped groove 4 of the lens frame 3 and, as a result, the three-dimensional configuration of the lens frame 3 cannot be measured.
To overcome this fault, an idea is proposed that the frame holding device is arranged such that one end portion, length-wise, of the apparatus is rotated upwardly and downwardly about a rotational axis at the other end portion of the apparatus, and a three-dimensional configuration of the lens frame is measured while inclining the frame holding device about the rotational axis depending on the curved angle of inclination of the eyeglass frame.
However, since the frame holding device is designed such that the rotational axis at the other end of the apparatus is served as a center of rotation, an amount of inclination (an amount of upward and downward rotational movement) of part of the lens frame close to the rotational axis of the eyeglass frame held by the frame holding device is reduced, and a favorable adjustment of inclination of part of the lens frame close to the eyeglass frame is not obtained easily.
Consequently, in case a three-dimensional configuration, for example, of a right-hand side eyeglass lens is measured, the left-hand side lens frame is situated on the side of the rotational axis for measuring the three-dimensional configuration of the right-hand side configuration of the right-hand side eyeglass lens. Thereafter, in case the three-dimensional configuration of the left-hand side lens is measured, the eyeglass frame is removed from the frame holding device and the three-dimensional configuration of the left-hand side lens frame is measured while situating the right-hand side lens frame on the side of the rotational axis.